Preheat oven to 450 - place the oven racks in the upper and lower thirds.

In a small bowl, whisk together mustard and ketchup.

In a medium bowl, mix together ground sirloin, egg, panko, 2 ounces (1/2 cup) cheddar, 1/2 teaspoon salt and 1/4 teaspoon fresh ground black pepper. Evenly divide the mixture into 4 portions - shape each into a 2" by 4" loaf and place them on a baking sheet coated with nonstick spray. Brush the loaves with the mustard mixture and sprinkle with the remaining cheddar.

On another baking sheet, add potatoes and toss with olive oil and season to taste with salt and fresh ground black pepper.

Place the pans into the oven and bake until the loaves have cooked through, about 15 to 20 minutes, rotating the sheets after 10 minutes. Remove the loaves and leave the potatoes inside until they are tender, about 5 more minutes.